Forsythia × intermedia 'Karl Sax'

RHS Plant Profile
forsythia 'Karl Sax'

Save a plant

Where do you want to save Forsythia × intermedia 'Karl Sax'?

Plants I own
Wishlist
Go to My Plants
forsythia 'Karl Sax' RHS / Joanna Kossak
forsythia 'Karl Sax' RHS / Joanna Kossak
forsythia 'Karl Sax' visionspictures.com
Shrubs

An upright shrub with arching branches and oval, partly toothed leaves. Bright yellow flowers are produced on bare stems in early spring

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1.5-2.5 metres

Max Spread

1.5-2.5 metres

Size

Time to Maturity
5–10 years
Max Spread
1.5-2.5 metres
Max Height
1.5-2.5 metres

Growing Conditions

Chalk Clay Loam Sand
Moisture
Moist but well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun Partial shade
Aspect
West–facing or South–facing or East–facing
Exposure
Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Oleaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy
Genus
Forsythia are deciduous shrubs with simple, occasionally lobed, leaves and short tubular yellow flowers with 4 spreading lobes, borne profusely before the leaves in spring
Name Status
Accepted

How to Grow

Cultivation

Grow in moist but well-drained soil in sun or partial shade

Propagation

Propagate by semi-hardwood cuttings

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Banks and slopes
  • Flower borders and beds
  • Wall side borders

Pruning

Pruning group 2

Pests

May be susceptible to birds eating the flower buds

Diseases

May be susceptible to honey fungus and forsythia gall